They will leave in their droves when other airlines start advertising and they have had their taste of flying... doen't sould llike good business to me.
Firstly we'll see if this actually happens or is just another BASSA exercise in wish fulfilment. I remember being told the only people applying to MF would be "skanks" and useless incompetents who couldn't get a job anywhere else. Now that we've seen them and they're actually very good, the next line of attack is "they'll all run off to the mythical better contracts freely available elsewhere ASAP". Again, we'll see.
Having said that I accept that what BA are trying to do is move the job of cabin crew away from being a 25-30 year career and into the area of short term (2-3 year) employment. With relatively low training costs and a large pool of applicants, this is, on the contrary, very good business.